Looks to be pretty extensive.
Source: http://www.pcgamer.com/gta-5-pc-graphics-options-in-full/
Video memory slider: shows you how much video memory is being used in MB.
Ignore suggested limits option: game detects your setup automatically, but you can push your system further if you like.
Options for screen type, aspect ratio and refresh rate.
DirectX Version Output monitor: 1-3
Anti-aliasing: FXAA, MSAA and Nvidia TXAA supported.
Pause game on focus loss.
Scaling bars for population density, population variety and distance scaling.
Texture quality: normal to very high.
Shader quality: normal to very high.
Shadow quality: normal to very high.
Reflection quality: normal to very high.
Reflection MSAA
Water quality: normal to very high.
Particles quality: normal to very high.
Grass quality: normal to very high.
Soft shadows options: softer, softest, AMD CHS, Nvidia PCSS
Post FX options: up to ultra.
Motion blur strength: scaling bar.
In-game depth of field effects: on/off.
Anisotropic filtering: up to x16 .
Ambient occlusion options.
Tesellation options.
Advanced graphics
Long shadows: on/off.
High resolution shadows: on/off.
High detail streaming while flying: on/off.
Extended distance scaling bar.
Extended shadow distance bar.
Benchmark testing.
Source: http://www.pcgamer.com/gta-5-pc-graphics-options-in-full/